Recent developments in telecommunication and semiconductor technologies facilitate the transfer of growing amounts of information over wireless networks.
Recent developments in telecommunication and semiconductor technologies facilitate the transfer of growing amounts of information over wireless networks.
Short-range ultra wide band wireless networks are being developed in order to allow wireless transmission of vast amounts of information between various devices.
Some of short-range ultra wide band wireless networks are characterized by a distributed architecture in which devices exchange information without being controlled by a central host or a base station.
FIG. 1 is a schematic illustration of two ultra wide band wireless networks (also referred to as personal access networks) 10 and 20, each including multiple devices that wirelessly communicate with each other. First network 10 includes first till fifth devices A-E 11-15 and the second network 20 includes sixth till eighth devices F-I 26-29.
Each of the ultra wide band wireless networks uses time division multiple access (TDMA) techniques in order to allow its devices to share a single channel.
FIG. 2 illustrates a typical TDMA frame 30. TDMA frame 30 includes multiple time-slots, such as beacon slots 14 and media access slots. The media access slots include distributed reservation protocol (DRP) slots 36 and prioritized contention access (PCA) slots 38. PCA slots are also referred to as PCA periods. DRP slots are also referred to as DRP periods. The TDMA frame is also referred to as super frame.
The beacon slots are used to synchronize devices to the TDMA frame 30. A typical beacon frame includes information that identifies the transmitting device. It also may include timing information representative of the start time of the TDMA frame 30.
The DRP slots 36 are coordinated between devices that belong to the same network and allow devices to reserve these slots in advance. During the PCA slots 38 devices that belong to the network compete for access based upon their transmission priority. It is noted that the allocation of media access time slots is dynamic and can change from one TDMA frame to another.
Typically, transmissions from devices during PCA slots are assigned by applying a carrier sense multiple access with collision avoidance (CSMA/CA) scheme. If a device requests to transmit over a wireless medium it has to check if the wireless medium is idle. If the wireless medium is idle, the device has to wait a random backoff period. This random backoff time is selected from a contention window that has a length that is related to the priority of the device. For higher-priority devices the contention window is shorter.
The transmission process is usually quite complex and includes many operations such as but not limited to forward correction encoding, interleaving, modulating and the like. A receiver must reverse the procedures applied by the transmitter.
Various techniques are applied in order to increase the reliability of wireless telecommunications. A first technique includes sending acknowledgement messages to indicate a reception of a certain information frame when performing point-to-point transmission. These acknowledgement messages can be sent per frame or per a group of frames. The former decreases the communication channel utilization but reduces communication error penalty. The acknowledgement transmission techniques (Imm-ACK and B-ACK) are not applied when performing multicast or broadcast transmission over ultra wide band wireless networks.
In some networks that include a central station and various clients or a master station and multiple slave stations various acknowledgment schemes were applied. The following U.S. patent, U.S. patent applications and PCT patent application, all being incorporated herein by reference, provide an example of some prior art methods and systems: U.S. patent application 2001/0051529 of Davies titled “Radio system and apparatus for, and method of, multicast communication”; U.S. Pat. No. 6,122,483 of Lo et al. titled “Method and apparatus for multicast messaging in a public satellite network”; U.S. patent application 2003/0145102 of Keller-Tuberg, titled “Facilitating improved reliability of internet group management protocol through the use of acknowledgment massages”; and PCT patent application WO2004/084488 of Lynch et al, titled “Method and apparatus for reliable multicast”.
It is noted that in some applications (such as but not limited to streaming video, sound, and the like) the performance and the user experience deteriorate significantly when the non-acknowledgement schemes are used with nominal channel conditions (˜1-8% Packet Error Ratio). Also, using acknowledge schemes in layers above the MAC layer (such as TCP/IP layers) increase significantly the latency and memory requirements, deteriorate the throughput, and in some cases make the application impractical if not impossible from implementation standpoint.
There is a need to increase the reliability of ultra wide band transmission while keeping the throughput high and implementation requirements overhead low, reducing transmission or reception of error penalty.